1. Field of the Invention
The present invention relates to signal processing, and more particularly, to a signal processing apparatus for and a method of reproducing a signal read from a predetermined channel by detecting a part of the signal in which an error occurs most frequently and correcting the errors in the signal.
2. Description of the Related Art
There are several well known methods of reproducing a signal read from a communication channel or a channel on a recording medium including: slicer threshold detection, partial response maximum likelihood (PRML), and decision feedback equalization (DFE). In the slicer threshold detection method, a waveform of a signal read from a channel is shaped by an analog equalizer, and then the signal value is compared with a reference level. That is, if the signal value is above a reference level, it is determined to be a one “1”, and if the signal value is below a reference level, it is determined to be a zero “0”.
FIG. 1 shows a configuration of a typical PRML system. Referring to FIG. 1, the PRML system includes an equalizer having a feed-forward filter and a least mean square (LMS) algorithm block 100 for adjusting the coefficient of the equalizer according to a feedback signal ek, an error detector 110, and a Viterbi decoder 120. The equalizer and LMS algorithm block 100 equalizes a signal yk from a channel (“channel signal”) to a desired form of channel response. Then, the error detector 110 detects errors from the equalized channel signal to output a corrected signal ak. The Viterbi decoder 120 takes into account all possible error paths to determine an optimal signal path, thereby estimating an original signal before the original signal passed through the channel.
FIG. 2 shows a configuration of a typical DFE system. Referring to FIG. 2, the DFE system includes first and second finite impulse response (FIR) filters 200 and 210 and a threshold determiner 220. The first FIR filter 200 is a feed-forward filter, and the second FIR filter 210 is a feed-back filter. A signal yk output from a channel is input into the first FIR filter 200. The threshold determiner 220 makes a temporary decision from the input signal and outputs the temporary decision value ak to the second FIR filter 210. The output values of the first and second FIR filters 200 and 210 are combined to change the temporary decision to a more reliable decision through a feedback signal ek.
Among the conventional signal detection methods described above, slicer threshold detection uses a simple slicer circuit but has low performance. Both the PRML and the DFE systems exhibit excellent performance but each has a large hardware complexity where the systems are realized with hardware. For example, the PRML system and the DFE system require a number of multipliers corresponding to the number of taps if the systems are implemented as a filter and a number of multipliers corresponding to about 2 times the number of filter taps times the number of filters in order to implement an adaptive algorithm. Thus, use of the PRML system or the DFE increases hardware complexity and decreases signal processing speed.